Contamination of early polio vaccine may be linked to rare tumours

The introduction of the Salk parenteral vaccine in the mid-1950s led to a dramatic decline in the incidence of poliomyelitis. By 1961, the majority of young adults in Britain and America had been immunised and the numbers of reported cases of poliomyelitis had fallen from 8000 a year to 100 a year.1 At that point in the mass immunisation programme, a contaminating virus was identified in the rhesus monkey kidney cells that were used to culture the poliovirus. It was named simian virus 40 (SV40). It was more resistant than poliovirus to chemical denaturation and survived into some vaccine samples. There are no reliable data about the proportion of batches that were contaminated with live SV40, and estimates range up to 30%.2 Early worries that the contaminant might be implicated in the development of human cancers have recently resurfaced.

SV40 was characterised as a double stranded DNA virus belonging to the group of papovaviruses. They …